The effect of ultrasonic waves on the nucleation of pure water and degassed water

In order to clarify the mechanism of nucleation of ice induced by ultrasound, ultrasonic waves have been applied to supercooled pure water and degassed water, respectively. For each experiment, water sample is cooled at a constant cooling rate of 0.15 °C/min and the ultrasonic waves are applied from the water temperature of 0 °C until the water in a sample vessel nucleates. This nucleation temperature is measured. The use of ultrasound increased the nucleation temperature of both degassed water and pure water. However, the undercooling temperature for pure water to nucleate is less than that of degassed water. It is concluded that cavitation and fluctuations of density, energy and temperature induced by ultrasound are factors that affect the nucleation of water. Cavitation is a major factor for sonocrystallisation of ice.     

超声手术刀声学系统设计和实验*

为兼顾阶梯型变幅杆的高放大系数以及曲线过渡变幅杆突变截面处的高疲劳强度,本文提出了一种最速曲线过渡段的超声刀换能器。首先,基于等效电路法,设计了夹心式压电换能器的基本结构。在此基础上,结合超声刀的工作条件和材料特性,对换能器基本结构进行精确设计;然后,利用FEM法和实验法获取了换能器纵振频率以及频率响应曲线,进一步证明了本文所设计换能器的有效性;最后,对所设计的换能器进行了一系列测试,结果表明：测定了无负载换能器谐振频率与输出端振幅,与设计目标、仿真结果相吻合;连接负载后凝血,切割效果良好。     

Physical field simulation of the ultrasonic radiation method: An investigation of the vessel,probe position and power

In this paper, the effects of ultrasonic probe position, vessel shape, and ultrasonic input power on the sound pressure distribution in the reactor were investigated by solving the Helmholtz equation using COMSOL Multiphysis^@ software. Three different types of glass containers were used in the study, which are beaker, Erlenmeyer flask, and round bottom flask. The maximum value of sound pressure in the three containers will gradually increase when the distance between the probe and the bottom of the container decreases. When the distance decreases, the area of the high acoustic pressure region in the round bottom flask does not change significantly, while the area of the high acoustic pressure region in the beaker and Erlenmeyer flask increases sharply, which means that the use of the round bottom flask can reduce the influence of the dead zone on the preparation of nanomaterials. In addition, the change in power increases the value of the peak negative acoustic pressure in the vessel, enhancing the response efficiency of ultrasonic cavitation.     

Effects of ultrasonic reactor design on sewage sludge disintegration

The impact of ultrasound (US) reactor design on cavitation intensity distribution and disintegration efficiency was studied for sewage sludge pre-treatment, using a US flatbed reactor of variable reaction chamber height (RCH, 20–100 mm). Mapping of cavitation intensity and treatment effects was conducted using (i) hydrophone measurements, (ii) aluminum foil tests, and (iii) soluble chemical oxygen demand (COD) analyses. The overall disintegration efficiency was evaluated based on average COD solubilization. The impact of flow on treatment (in)homogeneity was additionally examined using computational fluid dynamics (CFD). Results of all measurement techniques suggest that small RCHs (20 mm, for instance) enable uniform and intense treatments, while large RCHs, which are subjected to strong sound wave attenuation, entail inhomogeneous treatments where large fractions of substrate are no longer exposed to notable cavitation activity. For instance, COD solubilization (relative to alkaline hydrolysis) measured in the channel center dropped from 6.4% to zero as RCH widened from 20 mm to 100 mm. Flow-through sonication further aggravates treatment inhomogeneity due to the high flow rates in the low-cavitation channel centers. Overall disintegration efficiency declined with increasing RCH, showing a drop in average COD solubilization by 73% from RCH = 20 mm to RCH = 100 mm. The drop correlated with average cavitation noise levels (R² = 0.82), indicating that hydrophone measurements may be a suitable tool for US reactor design optimization. Overall, results suggest that reactor geometry has a critical impact on both treatment (in)homogeneity and treatment efficiency and that equal specific energy inputs do not imply equal US treatments.     

The cavitation erosion of ultrasonic sonotrode during large-scale metallic casting: Experiment and simulation

Ultrasonic sonotrodes play an essential role in transmitting power ultrasound into the large-scale metallic casting. However, cavitation erosion considerably impairs the in-service performance of ultrasonic sonotrodes, leading to marginal microstructural refinement. In this work, the cavitation erosion behaviour of ultrasonic sonotrodes in large-scale castings was explored using the industry-level experiments of Al alloy cylindrical ingots (i.e. 630 mm in diameter and 6000 mm in length). When introducing power ultrasound, severe cavitation erosion was found to reproducibly occur at some specific positions on ultrasonic sonotrodes. However, there is no cavitation erosion present on the ultrasonic sonotrodes that were not driven by electric generator. Vibratory examination showed cavitation erosion depended on the vibration state of ultrasonic sonotrodes. Moreover, a finite element (FE) model was developed to simulate the evolution and distribution of acoustic pressure in 3-D solidification volume. FE simulation results confirmed that significant dynamic interaction between sonotrodes and melts only happened at some specific positions corresponding to severe cavitation erosion. This work will allow for developing more advanced ultrasonic sonotrodes with better cavitation erosion-resistance, in particular for large-scale castings, from the perspectives of ultrasonic physics and mechanical design.     

船用超声液位传感器的分析与设计

介绍了一种船用某型超声液位传感器的基本结构和工作原理。在对脉冲式超声探头的轴向声压分布特点及其声透射强度分析研究的基础上,给出了该传感器的超声信号发射端与接收端之间距离d和压电晶片保护膜的壁厚δ值的确定方法。最后设计了一套超声液位传感器性能测试实验平台,对上述理论研究结论进行了实验验证。     

超声空化去毛刺的理论分析及数值仿真

随着制造业的不断发展,对产品的加工精度要求愈来愈高,然而微小毛刺的去除仍然是十分困难的。毛刺虽小但危害巨大。因此,有效去除毛刺已成为加工中不可或缺的工序。而超声波去毛刺法可以有效快速的去除复杂零件的微小毛刺,具有很高的实用价值。尽管超声波的相关理论日趋完善,但是超声去毛刺机理以及空化产生的高压对毛刺的影响缺乏一些理论参考。此文阐述了超声波去毛刺的基本原理,利用有限元软件ABAQUS对单个空化泡在毛刺上的溃灭过程进行数值仿真,证明了超声波去毛刺的可行性,通过实验验证,超声波能够有效的去除毛刺。其研究结果为进一步研究超声波去毛刺的理论提供了参考。     

Vibration characteristics of aluminum surface subjected to ultrasonic waves and their effect on wetting behavior of solder droplets

The vibration characteristics of an aluminum surface subjected to ultrasonic waves were investigated with a combination of numerical simulation and experimental testing. The wetting behavior of solder droplets on the vibrating aluminum surface was also examined. The results show that the vibration pattern of the aluminum surface is inhomogeneous. The amplitude of the aluminum surface exceeds the excitation amplitude in some zones, while the amplitude decreases nearly to zero in other zones. The distribution of the zero-amplitude zones is much less dependent on the strength of the vibration than on the location of the vibration source. The surface of the liquid solder vibrates at an ultrasonic frequency that is higher than the vibration source, and the amplitude of the liquid solder is almost twice that of the aluminum surface. The vibration of the surface of the base metal (liquid solder) correlates with the oxide film removal effect. Significant removal of the oxide film can be achieved within 2 s when the amplitude of the aluminum surface is higher than 5.4 μm or when the amplitude of the liquid solder surface is higher than 10.2 μm.     

水平连铸圆钢超声检测结果的信号处理

水平连铸圆钢为多晶种的不均匀粗晶材料，当采用超声波对其进行检测时，将产生较强的组织散射噪声，从而使得对缺陷回波的判断与评价无法进行本文采用分离频谱的方法对原始检测信号进行处理，再用截止地对缺陷回波进行恢复运算。实验结果本文所采用的方法能较为有效地消除原始检测信号中的组织噪声，从而提高超声检测的信噪比。     

Research on ultrasonic excitation for the removal of drilling fluid plug,paraffin deposition plug,polymer plug and inorganic scale plug for near-well ultrasonic processing technology

Near-well ultrasonic processing technology attracts more attention due to its simple operation, high adaptability, low cost and no pollution to the formation. Although this technology has been investigated in detail through laboratory experiments and field tests, systematic and intensive researches are absent for certain major aspects, such as whether ultrasonic excitation is better than chemical agent for any plugs removal; whether ultrasound-chemical combination plug removal technology has the best plugs removal effect. In this paper, the comparison of removing drilling fluid plug, paraffin deposition plug, polymer plug and inorganic scale plug using ultrasonic excitation, chemical agent and ultrasound-chemical combination plug removal technology is investigated. Results show that the initial core permeability and ultrasonic frequency play a significant role in plug removal. Ultrasonic excitation and chemical agent have different impact on different plugs. The comparison results show that the effect of removing any plugs using ultrasound-chemicals composite plug removal technology is obviously better than that using ultrasonic excitation or chemical agent alone. Such conclusion proves that ultrasonic excitation and chemical agent can cause synergetic effects.     

An experimental and modeling investigation of aluminum-based alloys and nanocomposites processed by ultrasonic cavitation processing

Some recent studies are showing that the microstructure and mechanical properties of manufactured components can be significantly improved when ceramic nanoparticles are used as reinforcement to form a metal-matrix-nano-composite (MMNC). During the fabrication of MMNCs, ultrasonic cavitation processing plays an important role in refining microstructure, dispersing nanoparticles and breaking up clusters of nanoparticles.     

Impact of ultrasonic treatment process on pour point of vegetable oils based liquid insulation

This study presents an application of ultrasonic technology in the high voltage liquid insulation domain towards the reduction of pour point of vegetable oil samples for the utilization of vegetable oils as liquid insulation in cold climate areas on power transformers. Pour point reduction has been achieved by processing the vegetable oil samples by using ultrasonic treatment process with 100 W and 30 kHz ultrasonic waves for various exposure times of 15, 30, 45 and 60 min. Edible vegetable oils such as sunflower oil, palm oil, sesame oil and non edible vegetable oils such as honge oil, neem oil and punna oil are considered as two categories of vegetable oils for this experimental investigation. Ultrasonic treatment process results in the reduction of pour point of vegetable oils to meet out the standard value of pour point for liquid insulation as per IEEE Standard C57.147, 2018. A significant reduction in pour point temperature of vegetable oil samples have been obtained with an increased exposure time. The obtained variations in pour point after exposure with ultrasonic waves may be due to the possible changes in crystallization kinetics of fatty acids components of vegetable oil samples due to energy input of ultrasonic waves. The experimental results have given a way towards the positive encouragement and development with ultrasonic treatment for achieving low pour point vegetable oils as liquid insulation in power transformers for applications on cold climatic areas.     

Effect of ultrasonic melt processing and Al-Ti-B on the microstructural refinement of recycled Al alloys

Refining the α-Al grain size and controlling the morphology of intermetallic phases during solidification of Al alloys using ultrasonic melt processing (USMP) and Al-Ti-B have been extensively used in academic and industry. While, their synergy effect on the formation of these phases has not yet clearly demonstrated. In this paper, the influence of USMP and Al-Ti-B on the solidified microstructure of multicomponent Al-4.5Cu-0.5Mn-0.5Mg-0.2Si-xFe alloys (x = 0.7, and 1.2 wt%) has been comparatively studied. The results show that the USMP + Al-Ti-B method produce a more profound refinement effect than the individual methods. In addition, the area of single Fe-rich phases in both alloys with USMP + Al-Ti-B are also refined compared with conventional methods. A mechanism is proposed for the refinement, which are the deagglomerated TiB₂ parties induced by USMP providing more effective nucleation sites for α-Al, and the refined interdendritic regions limited the growth of Fe-rich phases in the following eutectic reaction. Finally, the application of combined USMP + Al-Ti-B methods is feasible in microstructural refinement, resulting in the improving the casting soundness and mechanical properties of alloys.     

The influence of air content in water on ultrasonic cavitation field

Cavitation is a complex physical phenomenon affected by many factors, one of which is the gas dissolved in the medium. Researchers have given some efforts to the influence of gas content on sonoluminescence or some specific chemical reactions in and around the bubble, but limited work has been reported about the influence on the ultrasonic cavitation field distribution. In this work, the intensity distribution of the ultrasound field in a cleaning tank has been measured with the hydrophone. After analysed and visualised by MATLAB software, it was found that the cavitation intensity distribution in degassed water was much better than that in tap water. And further study proved that degassing process can improve the cavitation effect dramatically both in intensity and scope. Finally, the cavitation fields in mediums with different gas content were measured and the specific influence of air content on cavitation field was discussed.     

Model processes and cavitation indicators for a quantitative description of an ultrasonic cleaning vessel: Part I: experimental results

In this paper, four sensor types are presented for quantitative measurements in an ultrasonic cleaning vessel: (1) a hydrophone to measure spectral components of the sound field; (2) an aluminium foil technique as a model process for erosion; (3) a test tube filled with a solution of luminol to measure the emission of light; and (4) a test tube filled with potassium iodide solution to measure the oxidation of iodide. Thus a broad range of diverse cavitation effects is covered. The quantities were measured in dependence on three parameters: the electrical input power of the transducers, the temperature and the O₂ concentration of the water. To ensure constant environmental conditions, a flow system was built up which continuously exchanges the water in the vessel. The comparability of the data measured in subsequent measurement cycles is discussed and the influence of the different sensor types on the cavitation field is considered. Dependences on the three parameters are shown. A quantitative analysis of correlations between the data is carried out in the second part of the study (Koch and Jüschke, 2012 [1]).     

超声液位检测频率选择的理论计算和实验研究

非介入式超声液位检测中,中间层介质对反射回波强度有着显著的影响,为得到较强的检测回波信号,发射频率的选择是非常必要的。本文采用传输矩阵方法,对非介入式超声液位检测中声波在多层介质中的传播进行了研究,给出了反射回波声强与入射声波频率之间的关系,从理论上计算得到了最佳入射声波频率。实验结果与理论计算一致,由此为非介入式超声液位检测的频率选择提供了一有效的技术途径。     

提高超声测距分辨力的分析与设计

本文分析了分辨力误差的定量关系，并以此为指导选择和设计超声发射，接收，测时等电路以及数字滤波方法，提亢超声测距的精度和分辩力。     

An erosion sensor based on a quartz crystal microbalance for quantitative determination of the cleaning efficiency in an ultrasonic vessel

The efficiency of ultrasonic cleaning vessels cannot be measured directly in an easy way. In the presented work, a sensor is developed which quantitatively measures the ablation of a test layer. The sensor element is a quartz crystal which is coated with a sacrificial layer. Small changes in mass of this layer can be measured by a frequency shift of the crystal oscillation. For measurements, a 10 MHz AT-cut quartz crystal was used in a cleaning vessel working at 44.9 kHz. To determine the frequency shift by the ablation of the test layer, the quartz crystal was driven by a frequency generator sweeping the frequency in the range of the resonance frequency and a characteristic frequency was determined. The test layer which was applied to the quartz crystal consisted of silica microparticles suspended in varnish. In a preliminary experiment using a commercial cleaner it could be shown that significant changes in resonance frequency by cavitation effect could be detected. The initial frequency shift of the sacrificial layer is reproducible within 10%. The test layer can be adapted to the conditions of the cleaning vessel. By changing the electrical input power of the vessel, a threshold in the cavitation erosion was found.     

超声辅助滚压系统的设计与研究*

鉴于风力发电机组主轴的复杂工作情况和疲劳断裂失效形式,提出一种基于表面强化技术的超声辅助滚压加工系统;首先基于运动合成原理,获得了滚轮接触线的运动轨迹特征,并应用ANSYS/LS-DYNA软件分析了加工过程的特点;之后,基于一维振动理论、等效波长理论与牛顿迭代理论,推导了并求解了复合变幅杆的频率方程,实现了该复合变幅杆的纵向振动。通过对该变幅杆进行有限元仿真分析与振动特性测试,结果表明二者相对设计频率的偏差仅在0.817％以内。最后,通过对40Cr主轴进行超声辅助滚压测试,结果获得了粗糙度Ra 0.085μm和表面硬度32.2HRC的加工表面,较普通滚压加工粗糙度降低了69.1％,显微硬度提高了60％。